Paper stacking unit and image forming system

ABSTRACT

The paper stacking unit includes a paper stacking section on which the paper is stacked, a paper stacking mechanism which carries the paper to the paper stacking section on which the paper is stacked, and an abutment surface on which an end of the paper is abutted. The paper stacking mechanism includes a gripper member for holding the paper and a gripper moving mechanism. The gripper member holds the paper under the first holding force in a moving range from a holding position to a stacking position, and holds the paper under the second holding force upon the abutment of the end of the paper on the abutment surface from the stacking position.

CROSS-REFERENCE TO RELATED APPLICATIONS

The entire disclosure of Japanese Patent Application No. 2017-216210, filed on Nov. 9, 2017, is incorporated herein by reference in its entirety.

BACKGROUND Technological Field

The present invention relates to a paper stacking unit for stacking a sheet of paper, and an image forming system.

Description of the Related Art

There has been proposed an image forming system including an image forming apparatus for forming an image on a sheet of paper, and a paper stacking unit for stacking the paper having the image formed by the image forming apparatus.

Japanese Unexamined Patent Application Publication No. 2013-220937 (Patent Literature 1) discloses the technique for carrying the paper on which an image is formed, which includes the holding part for holding the paper ejected from a main body of the image forming apparatus, and a moving mechanism for moving the holding part along the moving path.

The paper stacking unit is required to have each end of sheets of paper aligned for the purpose of improving accuracy of the process performed by the post-processor, for example, stapling, punching, binding and the like, or allowing the user to facilitate the paper discharge operation. The paper stacking unit is configured to bring the paper end into abutment on the abutment surface for aligning the paper end so as to improve the paper alignment on the paper stacking section.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2013-220937

SUMMARY

The disclosed technique in Patent Literature 1 keeps the force for holding the paper thereinafter referred to as “holding force”) constant in the period from holding of the paper performed by the holding part until it is carried to the predetermined position. Assuming that the disclosed technique in Patent Literature 1 is applied to the paper stacking unit, if the holding force of the holding part is too strong, the paper may be bent upon abutment of the paper end on the abutment surface, resulting in the wrinkle of the paper. The bending of the paper may further cause the problem of deteriorating the paper alignment.

Meanwhile, if the holding force of the holding part is too weak, the paper may be slipped off from the holding part while it is carried. This may fail to carry the paper as intended, resulting in the problem of deteriorating the paper alignment.

It is an object of the present invention to provide the paper stacking unit capable of carrying the paper while being held under the appropriate force, and the image forming system.

To achieve the above-described object, according to an aspect of the present invention, a paper stacking unit reflecting one aspect of the present invention includes a paper stacking section on which a paper is stacked, a paper stacking mechanism which carries the paper to the paper stacking section on which the paper is stacked, and an abutment surface on which an end of the paper carried by the paper stacking mechanism is brought into abutment. The paper stacking mechanism includes a gripper member for holding the paper, and a gripper moving mechanism which moves the gripper member in a moving range at least from a holding position at which the paper is held to a stacking position at which the paper is stacked on the paper stacking section where the end of the paper held by the gripper member is brought into abutment on the abutment surface.

The gripper member makes a force for holding the paper switchable between a first holding force and a second holding force that is less than the first holding force. The paper is held under the first holding force in the moving range from the holding position to the stacking position. The paper is held under the second holding force upon the abutment of the end of the paper on the abutment surface from the stacking position.

The image forming system according to the present invention includes an image farming apparatus for forming an image on a paper, and the paper stacking unit as described above for receiving the paper carried from the image forming apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages and features provided by one or more embodiments of the invention will become more fully understood from the detailed description given hereinbelow and the appended drawings which are given by way of illustration only, and thus are not intended as a definition of the limits of the present invention:

FIG. 1 is a view schematically showing a structure of an image forming system according to an embodiment of the present invention;

FIG. 2 is a view schematically showing a structure of a paper stacking unit according to the embodiment the present invention;

FIG. 3 is a perspective view showing a paper stacking mechanism of the paper stacking unit according to the embodiment of the present invention;

FIG. 4 is a plan view showing the paper stacking mechanism of the paper stacking unit according to the embodiment of the present invention;

FIG. 5 is a perspective view showing a gripper member and a gripper moving mechanism of the paper stacking mechanism of the paper stacking unit according to the embodiment of the present invention;

FIG. 6 is a side view showing the gripper member and the gripper moving mechanism of the paper stacking mechanism of the paper stacking unit according to the embodiment of the present invention;

FIG. 7 is a perspective view showing the gripper member of the paper stacking mechanism of the paper stacking unit according to the embodiment of the present invention;

FIG. 8 is a side view showing the gripper member of the paper stacking mechanism of the paper stacking unit according to the embodiment of the present invention;

FIG. 9 is a partially perspective side view of the gripper member of the paper stacking mechanism of the paper stacking unit according to the embodiment of the present invention;

FIG. 10 is a side view showing a state representing an operation of an upper gripper of the gripper member of the paper stacking mechanism of the paper stacking unit according to the embodiment of the present invention;

FIG. 11 is a block diagram showing a structure of a control system for the image forming system according to the embodiment of the present invention;

FIGS. 12A and 12B are explanatory views representing operations of the paper stacking mechanism of the paper stacking unit according to the embodiment of the present invention;

FIGS. 13A and 13B are explanatory views representing operations of the paper stacking mechanism of the paper stacking unit according to the embodiment of the present invention;

FIGS. 14A and 14B are explanatory views representing operations of the paper stacking mechanism of the paper stacking unit according to the embodiment of the present invention;

FIGS. 15A and 15B are explanatory views representing operations of the paper stacking mechanism of the paper stacking unit according to the embodiment of the present invention;

FIG. 16 is a flowchart representing an example of the process for controlling moving speeds of the gripper member of the paper stacking mechanism of the paper stacking unit according to the embodiment of the present invention; and

FIG. 17 is a table showing the moving speeds of the gripper member of the paper stacking mechanism of the paper stacking unit according to the embodiment of the present invention, which are switchable in accordance with the paper type.

DETAILED DESCRIPTION OF EMBODIMENTS

A mode for implementing the paper stacking unit and the image forming system according to the present invention will be described referring to FIGS. 1 to 17. The common members shown in the respective drawings will be designated with the same codes. The scope of the present invention is not limited to the embodiment to be described below.

1. Embodiment 1-1. Structure of Image Forming System

An overall structure of the image forming system according to an embodiment (hereinafter referred to as example) of the present invention wilt be described. FIG. 1 is a view schematically showing a structure of an image forming system 1 according to the example.

As FIG. 1 shows, the image forming system 1 includes an image forming unit 10, a paper feed unit 20, and a paper stacking unit 30. The image forming system 1 has the paper feed unit 20, the image forming unit 10, and the paper stacking unit 30 which are sequentially arranged in order from the upstream side of to paper carrier path, and connected in series. The image forming system 1 allows the respective units to carry the paper thereamong, and to be inter-communicable with one another. The image forming system 1 according to the example is not limited to the structure as shown in FIG. 1, but may be configured to have a paper processor disposed between the image forming unit 10 and the paper stacking unit 30, or at the downstream side of the paper stacking unit 30 for processing the paper such as stapling, punching and binding.

The paper feed unit 20 includes a plurality of paper feed tray 21 (three trays in the example) which allow storage of a large amount of sheets of paper. The paper feed unit 20 feeds the paper stored in the paper feed tray 21 to the image forming unit 10.

The image forming unit 10 forms an image on the carried paper. The image forming unit 10 includes a plurality of paper feed trays 10 a, a carrier path 10 b, an image forming section 17, a fixing part 10 c, a reversing carrier path 10 d, and an operation display unit 14. The operation display unit 14 is disposed above the image forming unit 10. The operation display unit 14 is constituted by layering a display panel and a touch panel (operation part) to allow an operator to have operations and display at the upper part.

The paper feed trays 10 a are disposed at the lower part of the image forming unit 10. The carrier path 10 b carries papers fed from the paper feed trays 10 a or the paper feed unit 20. The image forming section 17 is disposed at an intermediate position on the carrier path 10 b.

The image forming section 17 includes image forming units corresponding to the respective colors (cyan, magenta, yellow, black, and the like), for example, so that the color toner image is formed on the paper. The fixing part 10 c is disposed at the downstream side of the image forming section 17 in the paper carrier direction (hereinafter referred to as “downstream side”) to receive the carried paper with the toner image.

The fixing part 10 c pressurizes and heats the carried paper so as to fix the toner image transferred onto the upper surface of the paper. The paper which has been subjected to the fixing process executed by the fixing part 10 c is carried to the paper stacking unit 30 along the carrier path 10 b, or carried to the reversing carrier path 10 d.

The carrier path 10 b is connected to the reversing carrier path 10 d that branches from the carrier path 10 b at the downstream side of the fixing part 10 c, and joins the carrier path 10 b at the upstream side of the image forming section 17. The reversing carrier path 10 d includes a reversing part for reversing the paper. The paper which has been reversed upside down or back and forth by the reversing part is carried to the carrier path 10 b at the upstream side of the image forming section 17, or carried to the carrier path 10 b at the downstream side of the fixing part 10 c while passing through the reversing carrier path 10 d. The paper ejected from the carrier path 10 b of the image forming unit 10 is carried to the paper stacking unit 30.

1-2. Example of Structure of Paper Stacking Unit 30

The structure of the paper stacking unit 30 will be described referring to FIGS. 2 to 4.

FIG. 2 is a view schematically showing the structure of the paper slacking unit 30.

The direction in which the paper is carried from the image forming unit 10 will be referred to as a carrier direction X, and the direction orthogonal both to the carrier direction X, and the up-and-down direction will be referred to as a width direction Y. The up-and-down direction orthogonal both to the carrier direction X and the width direction will be referred to as a vertical direction Z.

As FIGS. 1 and 2 show, the paper stacking unit 30 includes a paper detector 34, a plurality of carrier rollers 35, a paper stacking mechanism 37, a paper stacking section 38, and a carrier path 39. On the carrier path 39, the paper from the image forming unit 10 is carried to the paper stacking mechanism 37 and the paper stacking section 38. The carrier rollers 35 and the paper detector 34 are disposed on the carrier path 39. The paper detector 34 detects the paper that has been carried from the image forming unit 10.

[Paper Stacking Section]

The paper stacking section 38 includes a stacking tray 38 a, and a not shown mechanism for lifting the stacking tray 38 a in the vertical direction Z. Sheets of paper S that have been carried by the paper stacking mechanism 37 are stacked on the stacking tray 38 a. The paper stacking mechanism 37 is disposed at the upstream side of the paper stacking section 38 in the carrier direction X.

[Paper Stacking Mechanism]

FIG. 3 is a perspective view of the paper stacking mechanism 37. FIG. 4 is a plan view of the paper stacking mechanism 37.

As FIGS. 3 and 4 show, the paper stacking mechanism 37 includes a stack carrier unit 41, a casing 42, and a widthwise moving mechanism 43. The casing 42 is formed into a hollow rectangular parallelepiped shape. The stack carrier unit 41 is stored in the casing 42 via the widthwise moving mechanism 43. The casing 42 has an abutment surface 42 a abutted on an end part or a rear end of the paper S stacked on the paper stacking section 38 at the downstream side in the carrier direction X. The abutment surface 42 a faces the paper stacking section 38. Ejection roller pairs 51A, 51B and paper holders 52, 52 of the stack carrier unit 41, which will be described later can be seen from an opening formed in the abutment surface 42 a.

The widthwise moving mechanism 43 moveably supports the stack carrier unit 41 in the casing 42 in the width direction Y. The widthwise moving mechanism 43 includes guide shafts 43 a and a moving drive part 43 b. Both ends of the guide shalt 43 a in the width direction Y are fixed to the casing 42. The guide shaft 43 a pierces through the stack carrier unit 41 along the width direction Y so as to be moveably supported in the width direction Y. As the moving drive part 43 b is driven, the stack carrier unit 41 moves along the guide shaft 43 a in the width direction Y.

[Stack Carrier Unit]

The stack carrier unit 41 includes the two ejection roller pairs 51A, 51B, and the two paper holders 52, 52. Each of the ejection roller pairs 51A, 51B is constituted by two rollers facing with each other in the vertical direction Z. The two ejection roller pairs 51A, 51B are disposed at the upper end of the stock carrier unit 41 in the vertical direction Z at the corner end of the downstream side in the carrier direction X. The two ejection roller pairs 51A, 51B are disposed apart from each other in the width direction Y. The two ejection roller pairs 51A, 51B are rotatably driven by a roller driver 53 (see FIG. 11).

[Paper Holder]

Each of the two paper holders 52, 52 is disposed outside the corresponding one of the two ejection roller pairs 51A, 51B, respectively in the width direction Y. Each of the two paper holders 52, 52 has the same structure. The paper holder 52 includes a gripper member 61, a gripper moving mechanism 62, a gripper support member 63, and a cam member 64.

[Gripper Moving Mechanism]

FIGS. 5 and 6 show the gripper member 61 and the gripper moving mechanism 62.

As FIGS. 5 and 6 show, the gripper moving mechanism 62 includes a gripper driver 71, a first driven roller 73 a, a second driven roller 73 b, an endless drive belt 74, and a guide rail 75. The gripper driver 71 is formed as a stepping motor, for example, and configured to allow the rotating speed to be controllable in accordance with the pulse count.

The drive belt 74 is stretched to be laid among a drive shaft 72 of the gripper driver 71, the first driven roller 73 a, and the second driven roller 73 b. Upon driving of the gripper driver 71, the drive belt 74 is rotated while being supported with the drive shaft 72, the first driven roller 73 a, and the second driven roller 73 b.

The first driven roller 73 a and the second driven roller 73 b are disposed at the downstream side of the drive shaft 72 of the gripper driver 71 in the carrier direction X. The first driven roller 73 a and the second driven roller 73 b are disposed while facing with each other in the vertical direction Z. The first driven roller 73 a is disposed above the second driven roller 73 b in the vertical direction Z. The diameter of the drive shaft 72 is set to be larger than each diameter of the first driven roller 73 a and the second driven roller 73 b. The rotation center of the drive shaft 72 is located at an intermediate position between the first driven roller 73 a and the second driven roller 73 b in the vertical direction Z.

A first section T1 of the drive belt 74 wound around the drive shaft 72 is curved into the semicircular shape. A second section T2 of the drive belt 74 wound around from the drive shaft 72 to the first driven roller 73 a is substantially parallel to the carrier direction X. A third section T3 of the drive belt 74 wound around from the first driven roller 73 a to the second driven roller 73 b is substantially parallel to the vertical direction Z. A fourth section T4 of the drive belt 74 wound around from the second driven roller 73 b to the drive shaft 72 face the second section T2 in the vertical direction Z while being substantially parallel to the carrier direction X.

As FIG. 5 shows, the guide rail 75 is disposed at one end side of the drive belt 74 in the width direction Y. Likewise the drive belt 74, the guide rail 75 is of endless type, and formed into the similar shape to that of the drive belt 74 stretched to be laid among the drive shaft 72, the first driven roller 73 a, and the second driven roller 73 b.

The gripper member 61 is connected to the gripper moving mechanism 62 via a joint member 77. The joint member 77 includes a fixed part 77 a fixed to the drive belt 74, a guide roller 77 b. and a joint shaft 77 c. The joint shaft 77 c is fixed to the fixed part 77 a. The gripper member 61 is rotatably supported at an end of joint shaft 77 c, opposite the other end at the side of the fixed part 77 a. The guide roller 77 b is rotatably supported with the joint shaft 77 c.

The guide roller 77 b put around the joint shaft 77 c is disposed between the fixed part 77 a and the gripper member 61. The guide roller 77 b is slidably engaged with an outer circumferential surface of the guide rail 75 of the gripper moving mechanism 62. The above-described structure prevents rattling generated when the gripper moving mechanism 62 is driven to move the gripper member 61.

[Gripper Member]

FIG. 7 is a perspective view of the gripper member 61. FIG. 8 is a side view of the gripper member 61. FIG. 9 is a partially perspective side view of the gripper member 61. FIG. 10 is a side view showing the state where the gripper member 61 is operated.

As FIGS. 7 to 10 show, the gripper member 61 includes a lower gripper 81, an upper gripper 82, a first turning shaft 85, a second turning shaft 86, a first urging member 91, and a second urging member 92.

As shown in FIGS. 5 and 6, the lower gripper 81 is connected to the gripper moving mechanism 62 via the joint member 77. As FIGS. 7 and 8 show, the lower gripper 81 includes two slide rollers 88, 88. The two slide rollers 88, 88 are rotatably attached to both ends of the lower gripper 81, respectively in the width direction Y. The two slide rollers 88, 88 are disposed on the lower gripper 81 while being apart from each other in the carrier direction X.

The lower gripper 81 includes a holding surface 81 a which protrudes toward the downstream side in the carrier direction X from the part where the two slide rollers 88, 88 are disposed. The upper gripper 82 is rotatably supported via the first turning shaft 85 between the holding surface 81 a and the part of the lower gripper 81, at which the two slide rollers 88, 88 are disposed.

The upper gripper 82 is rotatably disposed above the lower gripper 81 at the upper end side in the vertical direction Z. The upper gripper 82 includes a first upper gripper piece 83 and a second upper gripper piece 84.

The first upper gripper piece 83 is formed into a substantially L-like shape. A roller 87 is rotatably supported at one end of the first upper gripper piece 83. The roller 87 abuts on the cam member 64 to be described later. The first turning shaft 85 is disposed at a bent part of the first upper gripper piece 83. The first upper gripper piece 83 is rotatably supported with the lower gripper 81 via the first turning shaft 85.

Upon attachment of the first upper gripper piece 83 to the lower gripper 81, one end of the first upper gripper piece 83 at a side of the roller 87 is positioned below the first turning shaft 85 in the vertical direction Z. The other end of the first upper gripper piece 83 protrudes toward the downstream side of the first turning shaft 85 in the carrier direction X. The ether end is positioned above the holding surface 81 a of the lower gripper 81 in the vertical direction Z.

As FIG. 9 shows, the first urging member 91 is attached to the first turning shaft 85. The first urging member 91 may be formed as a torsion coil spring, for example. The first urging member 91 urges the other end of the first upper gripper piece 83 toward the holding surface 81 a of the lower gripper 81.

As FIGS. 7 and 8 show, the second upper gripper piece 84 is rotatably supported with the other end of the first upper gripper piece 83 via the second turning shaft 86. The second upper gripper piece 84 protrudes toward the downstream side in the carrier direction X from the other end of the first upper gripper piece 83. The second upper gripper piece 84 faces the holding surface 81 a of the lower gripper 81 in the vertical direction Z. A tower end surface 84 a of the second upper gripper piece 84 in the vertical direction Z is brought into contact with or separated from the holding surface 81 a.

As FIG. 9 shows, the second urging member 92 is attached to the second turning shaft 86. Likewise the first urging member 91, the second urging member 92 is formed as the torsion coil spring, for example. The second urging member 92 urges the second upper gripper piece 84 toward the holding surface 81 a of the lower gripper 81. The urging force of the second urging member 92 is set to be less than that of the first urging member 91.

In this example, the torsion coil spring is employed for the first urging member 91 and the second urging member 92. However, arbitrary member may be employed without being limited to the one as described above. It is possible to employ various kinds of elastic member such as a compression coil spring, a plate spring, and a rubber.

Referring to FIG. 10, upon abutment of the roller 87 attached to the first upper gripper piece 83 on the cam member 64 (first cam piece 64 a as shown in FIG. 10) to be described later, the first upper gripper piece 83 turns around the first turning shaft 85 in the direction in which the other end of the first upper gripper piece 83 separates from the holding surface 810 of the tower gripper 81 against the urging force of the first urging member 91. At this timing, the second upper gripper piece 84 turns around the second turning shaft 86 in the direction in which the lower end surface 84 a approaches the holding surface 81 a of the lower gripper 81 under the urging force of the second urging member 92.

[Gripper Support Member]

As FIG. 3 shows, the gripper support member 63 is supported with the stack carrier unit 41 so as to be moveable in the vertical direction Z. The gripper member 61 is disposed on the upper surface of the gripper support member 63 in the vertical direction Z so that the gripper member 61 is moveable in the carrier direction X.

A slide rail 63 a is formed in an upper end of the gripper support member 63 in the vertical direction Z. The slide rail 63 a is a long hole which is open along the carrier direction X (see FIG. 12A). The two slide rollers 88, 88 attached to the lower gripper 81 of the gripper member 61 are slidably engaged with the slide rail 63 a. The above-described structure secures the posture of the lower gripper 81 to be stably held even if the gripper member 61 is moved in association with the rotating drive belt 74.

[Cam Member]

As FIG. 3 shows, the cam member 64 is disposed in the stuck carrier unit 41. The cam member 64 is positioned to face the gripper member 61 in the width direction Y. The cam member 64 includes a first cam piece 64 a and a second cam piece 64 b. Abutment of the roller 87 attached to the first upper gripper piece 83 on the first cam piece 64 a or the second cam piece 64 b causes the upper gripper 82 to turn around the first turning shaft 85.

If the roller 87 is brought into abutment on the first cam piece 64 a, the first upper gripper piece 83 of the upper gripper 82 turns so that the second upper gripper piece 84 is turned to bring the lower end surface 84 a into abutment on the holding surface 81 a of the lower gripper 81 (see FIGS. 15A and 15B). If the roller 87 is brought into abutment on the second cam piece 64 b, the first upper gripper piece 83 of the upper gripper 82 turns to the position at which the lower end surface 84 a of the second upper gripper piece 84 is completely separated from the holding surface 81 a of the lower gripper 81 (see FIGS. 12B and 13A).

In this example, the two paper holders 52, 52 are disposed outside the ejection roller pairs 51A, 51B, respectively in the width direction Y. The present invention is not limited to the above-described example. It is possible to dispose the two paper holders 52, 52 between the ejection roller pairs 51A, 51B in the width direction Y.

1-3. Example of Control System Structure

An example of the control system structure of the image forming system 1 will be described referring to FIG. 11.

FIG. 11 is a block diagram showing the structure of the control system for the respective components of the image forming system 1.

As FIG. 11 shows, the image forming system 1 has its components connected to a client terminal 50 via a network N. The client terminal 50 may be a personal computer, for example. Based on the user's input operation, the client terminal 50 generates a document or image data for image formation using the image forming application. The client terminal 50 exhibits functions of generating the image forming job including the image forming setting information (which may be called “job ticket”) and an image farming job that contains the image data, and outputting the image forming job to the image forming unit 10.

Upon reception of the image forming job output from the client terminal 50 via the network N, the image forming unit 10 outputs an image formed on the paper based on the image forming setting and the image forming data of the image forming job (hereinafter referred to as “image forming process”). The image forming unit 10 may be a multi-function peripheral (MFP) with various functions (image forming function, copying function, scanning function and the like).

The image forming unit 10 includes a CPU 11 as the control unit, a memory 12, an auxiliary storage 13, the operation display unit 14, a manuscript data processor 15, a RIP processor 16, the image forming section 17, and the communication I/F 18. The respective components are inter-communicably connected via the system bus.

The CPU (Central Processing Unit) 11 executes the process for controlling the respective operations of the components of the image forming unit 10, and the arithmetic process. The CPU 11 executes the respective functions according to the embodiment by reading program codes of the software for executing the functions from the auxiliary storage 13. The image forming unit 10 may be configured to include the processor such as an MPU instead of the CPU 11.

The memory 12 is a main storage, into which variables and parameters generated during the arithmetic processing are temporarily written. For example, the RAM (Random Access Memory) or the like may be employed for the memory 12.

The auxiliary storage 13 is a storage unit which supports the memory 12 by performing an auxiliary function. The auxiliary storage 13 has a mechanism generally capable of storing data for a long period of time. The auxiliary storage 13 stores the program that activates the image forming unit 10 in addition to the OS and various parameters.

The operation display unit 14 is formed by layering the touch panel, as the operation section on a flat panel display as the display section. The operation display unit 14 generates an operation signal in accordance with contents of the operation input from the user, and supplies the generated operation signal to the CPU 11. The operation display unit 14 displays the result of the processing executed by the CPU 11.

The manuscript data processor 15 analyzes the image forming job input to the image forming unit 10, and processes the submitted image forming data. Various image forming data processed by the manuscript data processor 15 are supplied to the RIP processor 16.

The RIP processor 16 reflects the image forming setting to the image forming data, and converts (RIP processing) the data into the language (PDL: Page Description Language) distinguishable by the image forming unit 10 so that the language is output. As the language distinguishable by the image forming unit 10, PCL, PostScript and the like may be employed.

The image forming section 17 forms an image on the paper based on the RIP processed image forming data which have been output from the RIP processor 16. The image Riming section 17 is formed as a printer engine.

The communication I/F 18, for example, NIC (Network Interface Card) is configured to allow transmission and reception of various data between the respective components via the network N.

It is possible to connect the controller having the manuscript data processor 15 and the RIP processor 16 to the network N so that the image forming data which have been processed by the manuscript data processor 15 and the RIP processor are input to the image forming unit 10 and the paper stacking unit 30, respectively.

The paper stacking unit 30 receives the image forming data from the image forming unit 10, and makes a judgement on needs of, for example, sizing and weighing of the carried paper, and the post-processing such as stapling, punching and binding.

The paper stacking unit 30 includes a CPU 31, a memory 32, an auxiliary storage 33, the paper detector 34, a communication I/F 36, and the paper stacking mechanism 37. The respective components are inter-communicably connected one another via the system bus.

The CPU 31 as an example of the control unit controls operations of the respective components of the paper stacking unit 30, and executes the arithmetic process. The CPU 31 executes the respective functions according to the embodiment by reading the program codes of the software for implementing the functions from the auxiliary storage 33. The paper stacking unit 30 may be configured to include the processor such as the MPU instead of the CPU 31.

The memory 32 is a main storage, into which variables and parameters generated during the arithmetic processing are temporarily written. For example, the RAM (Random Access Memory) or the like may be employed for the memory 32.

The auxiliary storage 33 is a storage unit which supports the memory 32 by performing an auxiliary function. The auxiliary storage 33 has a mechanism generally capable of storing data for a long period of time. The auxiliary storage 33 stores the program that activates the paper stacking unit 30 in addition to the OS and various parameters.

The paper detector 34 detects the paper S that has been carried to the carrier path 39 of the paper stacking unit 30. Upon detection of the paper S, the paper detector 34 outputs the detection information to the CPU 31. The CPU 31 controls operations of the carrier rollers 35, the paper stacking section 38 (see FIG. 1), and the paper stacking mechanism 37 based on the detection information from the paper detector 34.

The paper tacking mechanism 37 includes a roller driver 53 for rotatably driving the ejection roller pairs 51A, 51B (see FIGS. 2 and 3) and the paper holders 52. Based on the drive signal from the CPU 31, the roller driver 53 rotatably drives the ejection roller pairs 51A, 51B. The paper holder 52 includes a gripper driver 71. The paper holder 52 drives the gripper driver 71 based on the drive signal from the CPU. The above-described structure allows the gripper member 61 of the paper holder 52 to execute the paper holding operation and the paper stacking operation.

For example, a NIC (Network Interface Card) may be employed for the communication I/F 36 which is configured to allow transmission and reception of various data among the respective components via the network N.

2. Example of Operation Performed by Paper Stacking Mechanism 2-1. Staking Operation of Paper Stacking Mechanism

An example of stacking operations performed by the above-structured paper stacking mechanism 37 will be described referring to FIGS. 12A to 15B.

FIGS. 12A to 15B are explanatory views showing the example of operations of the paper stacking mechanism 37.

The gripper member 61 is retracted downward of the carrier path 39 in the vertical direction Z, on which the paper S passes as shown in FIG. 12A until the paper S is carried to the ejection roller pairs 51A, 51B of the paper stacking mechanism 37. This makes it possible to prevent the paper S from being in contact with the gripper member 61 upon carriage of the paper S to the ejection roller pairs 51A, 51B.

When the paper S is carried to the ejection roller pairs 51A, 51B after passing over the gripper member 61 in the vertical direction Z, the CPU 31 (see FIG. 11) drives the gripper moving mechanism 62 to rotate the drive belt 74 (counterclockwise in the example). Then the gripper member 61 connected to the drive belt 74 via the joint member 77 (see FIG. 5) moves to the position as shown in FIG. 12B in association with the rotating drive belt 74.

At this timing, the roller 87 attached to one end of the first upper gripper piece 83 abuts on the second cam piece 64 b of the cam member 64. Then the first upper gripper piece 83 turns around the first turning shaft 85 up to the position at which the second upper ripper piece 84 is completely separated from the lower gripper 81 against the urging force of the first urging member 91. The downstream side of the gripper member 61 in the carrier direction X is released.

Rotation of the drive belt 74 causes the gripper member 61 and the gripper support member 63 to move upward in the vertical direction Z. As the two slide rollers 88, 88 of the lower gripper 81 are engaged with the slide rail 63 a of the gripper support member 63, the posture of the lower gripper 81 is stably kept.

Referring to FIG. 13A, as the roller 87 abuts on the second cam piece 64 b of the cam member 64, the gripper member 61 moves in the state where the upper gripper 82 is separated from the lower gripper 81. The other end of the first upper gripper piece 83, and the second upper gripper piece 84 of the upper gripper 82 protrude upward in the vertical direction Z toward the carrier path 39 of the paper S.

As the drive belt 74 rotates, the gripper member 61 moves from the upstream side to the downstream side in the carrier direction X up to the holding position for holding the paper S. As FIG. 13B shows, when the roller 87 is disengaged from the second cam piece 64 b, the first upper gripper piece 83 of the upper gripper 82 turns around the first turning shaft 85 under the urging force of the first urging member 91. In other words, the first upper gripper piece 83 turns in the direction in which the other end approaches the lower gripper 81. Accordingly, the gripper member 61 allows the second upper gripper piece 84 of the upper gripper 82 and the lower gripper 81 to hold the rear end of the paper S in the carrier direction X.

In this timing, the force F1 (hereinafter referred to as “first holding force”) of the gripper member 61 for holding the paper S mainly becomes the urging force of the first urging member 91, and the frictional force of the second upper gripper piece 84 and the lower gripper 81 applied to the paper S. The first holding force F1 is set to be more than the inertia force generated as a result of change in the speed at which the paper S carried by the two ejection roller pairs 51A, 51B is discharged therefrom.

The gripper member 61 moves from the upstream side to the downstream side in the carrier direction X while holding the paper S. At this timing, the gripper member 61 slides on the upper surface of the gripper support member 63, and the slide rollers 88, 88 slide along the slide rail 63 a of the gripper support member 63.

Upon rotation of the two ejection roller pairs 51A, 51B, the paper S is ejected from the paper stacking mechanism 37 to the paper stacking section 38 (see FIG. 2) while being held with the gripper member 61. The first holding force F1 of the gripper member 61 is set to be more than the inertia force generated as a result of change in the speed at which the paper S is discharged from the two ejection roller pairs 51A, 51B. Therefore, as shown in FIG. 14A, the paper S may be prevented from being slipped off from the gripper member 61 when it is ejected from the two ejection roller pairs 51A, 51B.

Upon rotation of the drive belt 74, the gripper member 61 moves downward in the vertical direction Z as shown in FIG. 14B. The gripper support member 63 for supporting the gripper member 61 also mows downward in the vertical direction Z. The first holding force F1 of the gripper member 61 is set to be more than the inertia force applied to the paper S upon movement in the vertical direction. Accordingly, the paper S may be prevented from being slipped off from the gripper member 61 even in the case of the vertical movement thereof.

As FIG. 15A shows, the gripper member 61 moves to the stacking position at which the paper S is stacked on the stacking tray 38 a of the paper stacking section 38. Further rotation of the drive belt 74 moves the gripper member 61 from the downstream side to the upstream side in the carrier direction X. The rear end of the paper S held with the gripper member 61 in the carrier direction X abuts on the abutment surface 42 a. This makes it possible to align ends of the sheets of paper S.

When the gripper member 61 moves from the downstream side to the upstream side along the carrier direction X, the roller 87 attached to the fiat upper gripper piece 83 abuts on the first cam piece 64 a of the cam member 64. The first upper gripper piece 83 turns in the direction in which the other end of the first upper gripper piece 83 is separated from the lower gripper 81 against the urging force of the first urging member 91. Then the second upper gripper piece 84 is urged by the second urging member 92 so as to turn around the second turning shaft 86 toward the lower gripper 81.

The pressing three from the upper gripper 82 applied to the paper S becomes the urging force of the second urging member 92. As the urging force of the second urging member 92 is set to be less than the urging force of the first urging member 91, the force of the gripper member 61 for holding the paper S changes to the second holding force F2 that is less than the first holding force F1. The second holding force F2 is set to be more than the inertia force applied to the paper S as a result of change in the speed, which occurs when the gripper member 61 pulls the paper S toward the abutment surface 42 a. This makes it possible to prevent the paper S from slipping off from the gripper member 61 upon abutment of the rear end of the paper S on the abutment surface 42 a.

Upon further rotation of the drive belt 74, the gripper member 61 moves from the downstream side to the upstream side in the carrier direction X as shown in FIG. 15B so that the paper S is pulled out from between the second upper gripper piece 84 and the lower gripper 81. Accordingly, the paper S is stacked on the stacking tray 38 a while having its rear end abutted on the abutment surface 42 a.

The above-described second holding three F2 of the gripper member 61 is set to be less than the force which buckles the paper S abutted on the abutment surface 42 a. This makes it possible to prevent the paper S having the rear end abutted on the abutment surface 42 a from being bent and wrinkled when it is pulled from between the second upper gripper piece 84 and the lower gripper 81.

As described above, the paper stacking mechanism 37 according to the example is configured to hold the paper S under the first holding force F1 upon its carriage from the ejection roller pairs 51A, 51B to the stacking position, and to hold the paper S abutted on the abutment surface 42 a under the second holding force F2 upon its pulling from between the upper gripper 82 and the lower gripper 81. In other words, the force of the ripper member 61 for holding the paper S is made switchable between the first holding force F1 and the second holding force F2 so that the paper S is carried while being held under the appropriate force.

The above-described structure prevents the paper S to be carried while being held with the gripper member 61 from not only slipping off but also from being bent and wrinkled upon pulling out while being abutted on the abutment surface 42 a. As the structure is capable of preventing the paper S from slipping off from the gripper member 61 or being wrinkled, it is possible to stack the sheets of paper S on the stacking tray 38 a of the paper stacking section 38 in the state where ends of the sheets of paper S are aligned, thus improving alignment of the paper S.

2-2. Example of Controlling Moving Speed of Gripper Member 61

Referring to FIGS. 12A to 15B, it is possible to make the moving speed of the gripper member 61 variable without being limited to the case for keeping the moving speed constant.

An example of controlling the moving speed of the gripper member 61 will be described referring to FIG. 16.

FIG. 16 is a flowchart representing the example of controlling the moving speed of the gripper member 61.

The gripper driver 71 of the gripper moving mechanism 62 is formed as the stepping motor. It is therefore possible to control the moving speed of the gripper member 61 in accordance with the pulse count of the gripper driver 71.

FIG. 16 shows, the CPU 31 of the paper stacking unit 30 determines whether the paper S has been ejected from the image forming unit 10 to the paper stacking unit 30 by means of the paper detector 34 (step S11). If it is determined that the paper detector 34 has detected the paper S in step S11 (YES in step S11), the CPU 31 drives the gripper driver 71 at a high speed for the period corresponding to the predetermined pulse count (for example, 100 pulses). As FIGS. 13A and 13B show, the gripper 61 is moved at the high speed in a moving range from the holding position for holding the paper S to the stacking position as shown in FIG. 14B (step S12).

Then the CPU 31 drives the gripper driver 71 at the speed (low speed) lower than the speed set in step S12 for the period corresponding to the predetermined pulse count (for example, 100 pulses). As FIGS. 15A and 15B show, the gripper member 61 is moved at a low speed until completion of pulling out of the paper from the stacking position (step S13). It is possible to weaken the impact force generated upon abutment of the rear end of the paper S on the abutment surface 42 a by lowering the carrier speed upon the above-described abutment. This makes it possible to suppress bending and wrinkling of the paper S, improving alignment of the paper S.

The CPU 31 drives the gripper driver 71 at the same speed as the one set in step S12, or at the speed (high speed) higher than the one set in step S13 for the period corresponding to the predetermined pulse count (for example, 100 pulses). Accordingly, referring back to FIG. 12B from FIG. 15B, the gripper member 61 is moved at the high speed from completion of the pulling out of the paper S until its movement to the home position (step S14).

As steps S12 and S14 represent, the gripper member 61 is moved at the speed (high speed) higher than the speed set in step S13 except the timing of completing pulling out of the paper S abutted on the abutment surface 42 a from the gripper member 61 (step S13). This makes it possible to accelerate the speed of the processing executed by the paper stacking unit 30.

In the above-described example, the moving speed of the gripper member 61 is switched in accordance with the pulse count of the gripper driver 71, which is not limited thereto. For example, it is possible to switch the moving speed of the gripper member 61 based on the positional information of the gripper member 61 detected by a plurality of positional detection sensors provided in the stack carrier unit 41 for detecting positions of the gripper member 61. It is also possible to switch the moving speed of the gripper member 61 based on the above-described pulse count of the gripper driver 71 combined with the positional information from the positional detection sensors. This makes it possible to improve accuracy of the timing for switching the moving speed of the gripper member 61.

The moving speed of the gripper member 61 may be controlled in accordance with the type of the paper S to be carried without being limited to the example as described above. Being held and carried by the gripper member 61, the thick paper is likely to be slipped off therefrom, but unlikely to be buckled. Meanwhile, the thin paper is unlikely to be slipped off from the gripper member 61, but likely to be buckled.

FIG. 17 is a table representing the moving speeds of the gripper member 61 in accordance with the paper type.

As FIG. 17 shows, the CPU 31 changes the moving speed of the gripper member 61 based on the paper type information from the paper type detection sensor for detecting the paper type of the paper S, or from the image forming unit 10. In the case of the thick paper, the gripper member 61 is moved at a medium speed from the second section T2 to the third section T3 as shown in FIG. 6, that is, until the paper S held by the gripper member 61 is carried to the stacking position. Even if the thick paper is carried, it is possible to prevent the paper from being slipped off from the gripper member 61. The gripper member 61 is moved at the medium speed in the fourth section T4, similar to the speed set in the range from the second section T2 to the third section T3, that is, until the paper S held by the gripper member 61 is pulled out while being abutted on the abutment surface 42 a.

Meanwhile, in the case of the thin paper, the gripper member 61 is moved at the high speed higher than the medium speed in the range from the second section T2 to the third section T3, that is, until the paper S held by the gripper member 61 is carried to the stacking position. The gripper member 61 is then moved at the low speed lower than the medium speed in the fourth section 14, that is, until the paper S held by the gripper member 61 is pulled out while being abutted on the abutment surface 42 a. This makes it possible to suppress bending and wrinkling of the paper even if the thin paper likely to be buckled is brought into abutment on the abutment surface 42 a.

Preferably, each time period taken for moving the gripper member 61 one round when using the thick paper and the thin paper is set to be substantially the same in order to secure the processing capabilities of the paper stacking unit 30. In the first section T1 as shown in FIG. 6, the paper S is not held by the gripper member 61. Therefore, the moving time is hardly influenced by the type of the carried paper S. It is preferable to move the gripper member 61 at the high speed in the first section T1 so as to improve the processing capabilities of the paper stacking unit 30.

The effects derived from the exemplified paper stacking unit and the image forming system have been described and illustrated in detail. However, the paper stacking unit and the image forming system according to the present invention are not limited to those described above, but may be variously modified so long as they do not deviate from the scope of the invention described in the appended claims.

In the above-described embodiment, four image forming units are used for forming the color image. However, the image forming apparatus according to the present invention may be configured to use the single image forming section for forming a monochromatic image. As the image forming apparatus, it is possible to employ not only the copy machine but also the printer, facsimile machine, or multi-function peripheral with various functions.

In the above-described embodiment, the CPU 31 of the paper stacking unit 30 serves to control the paper stacking mechanism 37. However, the present invention is not limited to the one as described above. For example, it is possible to control the paper stacking mechanism 37 by the CPU 11 of the image forming unit 10.

The terms such as “parallel” and “orthogonal” used in the description refer not only to the “parallel” and “orthogonal” according to the exact meanings but also to those falling in the broad range including “substantially parallel” and “substantially orthogonal” so long as the relevant functions are implemented.

REFERENCE SIGNS LIST

-   1 . . . image forming system, 10 . . . image forming unit, 11 . . .     CPU (control unit), 30 . . . paper stacking unit, 31 . . . CPU     (control unit), 34 . . . paper detector, 35 . . . carrier roller, 37     . . . paper stacking mechanism, 38 . . . paper stacking section, 38     a . . . stacking tray, 39 . . . carrier path, 41 . . . stack carrier     unit, 42 . . . casing, 42 a . . . abutment surface, 51A, 51B . . .     ejection roller pair, 52 . . . paper holder, 53 . . . roller driver,     61 . . . gripper member, 62 . . . gripper moving mechanism, 63 . . .     gripper support member, 64 . . . cam member, 64 a . . . first cam     piece, 64 b . . . second cam piece, 71 . . . gripper driver, 72 . .     . drive shaft, 73 a . . . first driven roller, 73 b . . . second     driven roller, 74 . . . drive belt, 75 . . . guide rail, 77 . . .     joint member, lower gripper, 81 a . . . holding surface, 82 . . .     upper gripper, 83 . . . first upper gripper piece, 84 . . . second     upper gripper piece, 84 a . . . lower end surface, 85 . . . first     turning shaft, 86 . . . second turning shaft, 87 . . . roller, 91 .     . . first urging member, 92 . . . second urging member, F1 . . .     first holding force, F2 . . . second holding force, T1 . . . first     section, T2 . . . second section, T3 . . . third section, T4 . . .     fourth section 

What is claimed is:
 1. A paper stacking unit comprising: a paper stacking section on which a paper is stacked; a paper stacking mechanism which carries the paper to the paper stacking section on which the paper is stacked; and an abutment surface on which an end of the paper carried by the paper stacking mechanism is brought into abutment, wherein: the paper stacking mechanism includes a gripper member for holding the paper, and a gripper moving mechanism which moves the gripper member in a moving range at least from a holding position at which the paper is held to a stacking position at which the paper is stacked on the paper stacking section where the end of the paper held by the gripper member is brought into abutment on the abutment surface; the gripper member makes a force for holding the paper switchable between a first holding force and a second holding force that is less than the first holding force; and the gripper member holds the paper under the first holding force in the moving range from the holding position to the stacking position, and holds the paper under the second holding force upon the abutment of the end of the paper on the abutment surface from the stacking position.
 2. The paper stacking unit according to claim 1, wherein: the gripper member includes a lower gripper connected to the gripper moving mechanism via a joint member, and an upper gripper rotatably supported with the lower gripper via a first turning shaft; the upper gripper includes a first upper gripper piece rotatably supported with the lower gripper via the first turning shaft, a second upper gripper piece rotatably supported with the first upper gripper piece via a second turning shaft, a first urging member for urging an end of the first upper gripper piece at a side of the second upper gripper piece toward the lower gripper, and a second urging member for urging the second upper gripper piece toward the lower gripper; and an urging force of the second urging member is set to be less than an urging force of the first urging member.
 3. The paper stacking unit according to claim 2, wherein: a roller is attached to an end of the first upper gripper piece, opposite the end at the side of the second upper gripper piece, the first turning shaft being interposed between both ends of the first upper gripper piece; the paper stacking mechanism includes a cam member to be abutted on the roller; and the first upper gripper piece turns in a direction in which the end at the side of the second upper gripper piece is separated from the lower gripper against the urging force of the first urging member upon abutment of the roller on the cam member.
 4. The paper stacking unit according to claim 1, comprising a control unit for controlling an operation to drive the gripper moving mechanism so that a moving speed of the gripper member is controlled.
 5. The paper stacking unit according to claim 4, wherein the control unit controls the gripper moving mechanism to set a moving speed of the gripper member upon the abutment of the end of the paper on the abutment surface from the stacking position to be lower than the moving speed of the gripper member in the moving range from the holding position to the slacking position.
 6. The paper stacking unit according to claim 5, wherein the control unit controls the gripper moving mechanism to set the moving speed of the gripper member upon returning back to the holding position from the abutment of the end of the paper on the abutment surface to be higher than the moving speed of the gripper member upon the abutment of the end of the paper on the abutment surface from the stacking position.
 7. The paper stacking unit according to claim 4, wherein the control unit controls a movement of the gripper member in accordance with a type of the paper to be carried.
 8. An image forming system comprising: an image forming apparatus for forming an image on a paper; and the paper stacking unit according to claim 1, to which the paper is carried from the image forming apparatus. 